U.S. patent number 5,727,421 [Application Number 08/386,566] was granted by the patent office on 1998-03-17 for apparatus and method for providing leak proof sealing between a metal rod and a plastic housing molded there around.
This patent grant is currently assigned to IMI Cornelius Inc.. Invention is credited to George W. Murphy.
United States Patent |
5,727,421 |
Murphy |
March 17, 1998 |
Apparatus and method for providing leak proof sealing between a
metal rod and a plastic housing molded there around
Abstract
An apparatus and method for providing liquid and gas proof
sealing between a metal rod and a plastic housing molded there
around. The rod includes a plurality of annular intrusions or
protrusions along a length thereof. The plastic material is formed
around the rod and the annular intrusions or protrusions. After the
plastic material has cooled the rod is translated linearly with
respect thereto whereby the annular intrusions or protrusions cause
a cold flow movement or disruption of the plastic material. This
movement results in a liquid and gas tight sealing between the rod
and the plastic housing. The invention herein has particular
application for liquid level sensing probes located within gas
pressurized vessels. In such examples the rod or rods are used for
sensing liquid level by means of electrical conductivity with the
sensed liquid. The sealing between the rod and plastic housing
prevents the contained pressurized liquid and gas from escaping the
vessel by flowing between the sensing rod or rods and their
respective plastic housing.
Inventors: |
Murphy; George W. (Elk River,
MN) |
Assignee: |
IMI Cornelius Inc. (Anoka,
MN)
|
Family
ID: |
23526131 |
Appl.
No.: |
08/386,566 |
Filed: |
February 10, 1995 |
Current U.S.
Class: |
73/304R;
73/866.5; 439/271; 340/620; 200/190; 439/913 |
Current CPC
Class: |
G01F
23/242 (20130101); H01R 13/521 (20130101); Y10S
439/913 (20130101) |
Current International
Class: |
G01F
23/24 (20060101); H01R 13/52 (20060101); G01F
023/00 (); H01H 029/00 (); H01R 004/48 (); H01R
013/52 () |
Field of
Search: |
;439/271,433,434,913
;200/190 ;340/620 ;73/34R,866.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Worth; Willie Morris
Attorney, Agent or Firm: Hakanson; Sten Erik
Claims
I claim:
1. A liquid level sensing probe for sealable engagement with a
container holding a liquid under pressure, comprising:
first and second rods each having one or more annular material
displacing structures along a length thereof,
a housing body made of a plastic material molded around the
rods,
one or more points of annular sealing engagement between the
annular displacing structures and the plastic material of the
housing resulting from linear translating of the first and second
rods with respect to the housing resulting in a cold flow
displacement of the plastic for forming the one or more points of
annular sealing engagement, and where after the linear translating
the first and second rods each have first probe ends extending from
a housing first end, and the housing having a sealing structure for
providing liquid tight sealing securing of the probe to the
container wherein the first housing end is retained within the
container.
2. The liquid level sensing probe as defined in claim 1, and the
rods each having second ends extending adjacent an exterior surface
of the plastic housing for permitting electrical connection
thereto.
3. The liquid level sensing probe as defined in claim 2, and the
plastic housing exterior surface for releasably receiving a plug
for facilitating the electrical connection to the probe second ends
and where the plug is releasably receivable in only one
position.
4. The liquid level sensing probe as defined in claim 1, wherein
the annular displacing structures each include annular groove
portions.
5. The liquid level sensing probe as defined in claim 1, wherein
the plastic material of the housing is electrically insulating.
6. The liquid level sensing probe as defined in claim 3, wherein
the annular displacing structures each include annular groove
portions.
7. The liquid level sensing probe as defined in claim 6, wherein
the plastic material of the housing is electrically insulating.
8. A carbonated water level sensing probe for sealable engagement
with a carbonator, comprising:
first and second rods each having one or more annular material
displacing structures along a length thereof,
a housing body made of an electrically insulating plastic material
molded around the rods,
one or more points of annular sealing engagement between the
annular displacing structures and the plastic material of the
housing resulting from linear translating of the first and second
rods with respect to the housing resulting in a cold flow
displacement of the plastic for forming the one or more points of
annular sealing engagement, and where after the linear translating
the first and second rods each have first probe ends extending from
a housing first end and where the first and second rods each have a
second end extending adjacent an exterior surface of the plastic
housing for permitting connection thereto of an electrically
operated conductivity sensor, and
the plastic housing having a sealing structure for providing liquid
and gas tight sealing securing of the probe to the carbonator
wherein the first housing end is retained within the
carbonator.
9. The liquid level sensing probe as defined in claim 8, and the
plastic housing exterior surface for releasably receiving a plug
for facilitating the connection to the conductivity sensor and
where the plug is releasably receivable in only one position.
10. The liquid level sensing probe as defined in claim 8, wherein
the annular displacing structures each include annular groove
portions.
11. The liquid level sensing probe as defined in claim 9, wherein
the annular displacing structures each include annular groove
portions.
Description
FIELD OF THE INVENTION
The present invention relates generally to methods and apparatus
for forming a plastic housing around an metal rod wherein such rod
is, for example electrified, as in a liquid level sensing device,
and in particular to such methods and apparatus wherein the rod
forms a liquid and gas tight seal between itself and the plastic
housing formed there around.
BACKGROUND OF THE INVENTION
It is well understood that molding plastic around a metal object
can involve certain problems relating to the differing physical
properties of the two substances, such as heat expansion and
contraction, heat capacity, and so forth. These differences can be
particularly challenging in the manufacture of, for example, liquid
level sensing probes. Such probes are well known in the art, and
can include a pair of electrically conductive rods at differing
levels for detecting the level of a liquid within a closed
container. Detection of the liquid level is generally accomplished
by detecting electrical flow between the rods and the container as
conducted by the liquid contained therein. The rods must then be
electrically isolated from each other and from the container. This
is usually done by molding the rods within a solid plastic housing.
Due to the above stated differing physical properties of metal and
plastic, it has long been recognized that the rods and the housing,
upon cooling, will not always have formed a liquid or gas tight
seal there between. This lack of binding between the two substances
is primarily the result of the greater shrinkage of the plastic as
it cools causing it to pull away and form gaps between itself the
metal rod. Thus, water or gas can move along the rod in those gaps
and can eventually flow out of the container. This problem is, of
course, exacerbated in applications where the container interior is
pressurized.
An example of a liquid level sensing probe used in a pressurized
container is seen in carbonated drink dispensing machines where the
water level in a pressurized carbonator tank must be continually
monitored. Leakage of water and carbon dioxide gas in these
applications can result in loss of pressure, corrosion of interior
components of the machine and shorting of the sensing rods thereby
causing reading errors.
Various strategies have been employed in the art to prevent this
liquid and gas leakage. Attempts have been made to encapsulate the
rods, or to use metal inserts within various compounds such as
epoxy resins. One strategy has been to provide for a "tortured
path" wherein the rod has a plurality of bends resulting in a
"zigzag" structure as it extends through the plastic body from one
end to the other thereof. However, such approaches have met with
limited success as they do not address the fundamental problem of
gap formation as the plastic cools. This strategy decreases
somewhat the chance that a pathway from one end of the rod to the
other will result, but does not serve to greatly minimize the
problem. As a result, a liquid or gas will eventually flow along
the length of any path regardless of how convoluted, if a
continuous space exists between the rod and the plastic.
Another approach to minimize this leakage problem has been simply
one involving the basics of plastic molding technique, such as
selecting a plastic with minimal shrinkage characteristics and
cooling the plastic at various rates. Unfortunately, the most
desirable plastic from a shrinkage point of view may not be usable
in the particular application, e.g. In a beverage dispenser
application the plastic may not be food compatible. Regardless,
these approaches also do not address the fundamental difference in
shrinkage between the plastic and the metal.
Accordingly, it would be very desirable to have a method and
apparatus for molding of plastic around a metal object, such as in
the example of a liquid level sensor, where liquid and gas proof
adhesion between the metal and plastic is provided for.
SUMMARY OF THE INVENTION
The present invention is an apparatus and method for providing
liquid and gas proof sealing between a metal rod and a plastic
housing molded there around. An example of an application of the
present invention can be illustrated in the case of a liquid level
sensing probe for use in determining the level of water in a
carbonator of a beverage dispensing machine. A carbonator, as is
known in the relevant art, comprises a sealed tank into which water
and carbon dioxide gas are delivered under pressure so that
carbonated water is formed therein. The carbonated water can then
be dispensed therefrom to form a beverage, as is also well
understood. Since the carbonated water is periodically withdrawn
therefrom, water and carbon dioxide gas must be added to replace it
so that more carbonated water can be formed. A liquid level sensing
probe is then used to determine when to pump in more water.
The carbonator water level sensor has a rod housing body consisting
of a solid plastic molded around a pair of level sensing rods. The
housing body includes threads and an o-ring for providing sealable
releasable engagement with a threaded hole in the carbonator tank.
When so secured to the tank, the housing has a connection end
extending exterior thereof for providing electrical connection of
the rods to a control/electrical sensing means, and an interior
portion extending there within. The rods consist of metal and
extend out of the housing interior portion for contacting the water
within the tank, and extend out of the housing connection end for
facilitating the above mentioned connection to the control means.
And each rod has one or more annular intrusions or protrusions
comprising wedge means there around along the length thereof.
After molding of the housing around the rod, and after the plastic
has cooled, the rods are both individually pushed further into the
housing body in a direction from the housing exterior portion to
the housing interior portion. In particular, each rod is pushed
whereby the annular intrusions or protrusions thereof provide for a
wedge-like sealing engagement between the rods and the surrounding
plastic housing material. This cold flow sealing between each of
the rod and the surrounding housing plastic material in the
vicinity of each annular intrusion or protrusion provides for a
plurality of fluid tight seals around the rods along the length
thereof.
A further aspect of the present invention concerns a specific
structure of the housing exterior portion. This exterior portion is
formed to receive a plug for connecting the rods to the
control/electrical sensing means. Moreover, the exterior portion is
designed to minimize any liquid connection between the exterior
probe ends that could occur as the result of condensation thereon
and result in erratic operation thereof.
DESCRIPTION OF THE DRAWINGS
A further understanding of the structure, operation, and objects
and advantages of the present invention can be had by referring to
the following detailed description which refers to the following
figures, wherein:
FIG. 1 shows a partial cross-sectional front plan view of the probe
of the present invention.
FIG. 2 shows a front plan view of the sensor of the present
invention secured to a carbonator tank subsequent to translation to
the rods with respect to the plastic housing.
FIG. 3 shows a top plan view along lines 3--3 of FIG. 1.
FIG. 4 shows a partial cross-sectional view along lines 4--4 of
FIG. 1.
FIG. 5 shows a cross-sectional view along lines 5--5 of FIG. 1.
FIG. 6 shows an enlarged cross-sectional view of a housing body and
rod after molding but prior to translation of the rod with respect
to the housing body.
FIG. 7 shows the housing and rod of FIG. 6 after translation of the
rod with respect to the housing body.
FIG. 8 shows an embodiment of a rod of the present invention.
FIG. 9 shows an alternate embodiment of a rod of the present
invention.
FIG. 10 shows an alternate embodiment of a rod of the present
invention.
DETAILED DESCRIPTION
The method and apparatus of the present invention can be described
in the context of liquid level sensor as used with a carbonator in
a beverage dispensing machine. As is known in the art, a sensor of
this type includes a structural or rod retaining portion that is
physically secured to the carbonator tank and a generally remotely
located electronic control portion electrically connected to the
rod retaining portion. Such a rod retaining portion is seen in
FIGS. 1 and 2 and generally referred to by the numeral 10. Rod
retaining portion 10 includes a molded plastic body 12 formed
around a pair of metal rods 14 and 16 extending the length thereof.
Rods 14 and 16 have liquid contacting ends 14a and 16a respectively
and electrical connecting ends 14b and 16b respectively.
Body 12 includes a threaded portion 26 separating a head portion 28
from a lower portion 30. Head portion 28 includes a hexagonal
flange 32 for facilitating the threaded engaging of sensor 10 with
a carbonator 33. As is understood by those of skill, an o-ring 34
is used to provide for a water tight sealing engagement between
sensor 10 and carbonator 33. As seen by also referring to FIGS. 3
and 4, head 28 includes a pair of plug receptacle sockets 36 and
38. Sockets 36 and 38 have interior perimeter surfaces 36a and 38a
having different geometry's. The perimeter of each socket surface
36a and 38a is defined by an upwardly extending flange 40. A
further pair of triangularly shaped flanges 42 and 44 are integral
with and secured to flange 40 as well as to hex flange 32. As seen
as referring to FIG. 4, socket flange 40 has a top surface 46, and
also includes a return 48 extending therefrom adjacent top surface
46. As is understood by those of skill, sockets 36 and 38 are
designed to receive a plug 50. In particular, plug 50 includes a
pair of socket inserts 52 and 54 constructed to have an exterior
surface geometry complementary to that of sockets 36 and 38
respectively to provide for specific insertion and cooperation with
sockets 36 and 38. In this manner, the correct polarity connection
of plug 50 with sensor 10 can be maintained. Sockets 52 and 54
provide for electrical connection between wires 56 and 58 and rod
ends 14b and 16b respectively. Wires 56 and 58 then provide
connection to and electronic control and power source, not shown.
As is also understood by those of skill, a flexible arm 60 on plug
50 provides for releasable securing of plug 50 with head 28 by snap
fitting interaction therewith with return 48.
The structure of rods 14 and 16 can be seen in greater detail in
FIGS. 6 and 8. Each rod 14 and 16 is structurally identical except
for being different overall lengths. This difference in length, as
is known in the art, provides for the needed differential in liquid
level sensing ability. The structure of rod 16, which will be
understood to apply as well to rod 14, includes a plurality of
frusto-conical surfaces 70 tapering to a shoulder 72. This creates
a plurality of annular areas 74 around each surface 70. These
annular areas can be understood as being the difference between the
nominal or maximum diameter 76 of each rod 16 and the minimum
diameters 78 seen at the intersection of the tapered end of each
surface 70 and its corresponding shoulder 72, i.e., that portion of
material of rod 16 that has been removed to create each surface 70.
Such removal can be accomplished by turning the rod and grinding
the material away. Each rod 14 and 16 is molded within body 12
wherein the plastic material of which during molding thereof flows
around and contacts each of the surfaces 70 thereby "filling" the
annular areas 74.
As stated, body 12 is manufactured by the molding of the plastic
material thereof around rods 14 and 16. In particular, rods 14 and
16 are positioned so that after cooling of the plastic material,
tip ends 14b and 16b are positioned to extend a short distance
above surface 46, as seen in FIG. 1. Rods 14 and 16 are then
further inserted into sensor body 10 wherein tip ends 14b and 16b
are then positioned flush with top surface 46, as seen in FIG. 2.
As a consequence thereof, tip ends 14a and 16a are necessarily
extended further from body 12 as is indicated by the ghost outlines
in FIG. 1, and as seen in FIG. 2. The reason for this further
insertion after cooling of the plastic material around rods 14 and
16 can be had by referring to FIGS. 6 and 7. As seen therein,
movement of rods 14 and 16 in the direction of Arrow A in FIG. 6
causes each frusto-conical surface 70 to act as a wedge pushing
against the plastic material located immediately around it, and in
particular, that material occupying grooves 74. Due to the angle of
inclination thereof, each frusto-conical surface 70 acts as a wedge
forcing tight contact between itself and that plastic material. As
a result thereof, that is, after the linear translation of rods 14
and 16 with respect to the plastic material there around, a tight
fit between each conical surface 70 and the plastic forming body 12
is positively established. It will be understood by those of skill
that the elasticity of the plastic permits this "cold" flow of
material. Also, as seen in FIG. 7, such movement can result in a
slight outward bulging as indicated by numerals 80, however the
presence or absence of such bulging is purely a matter of the
thickness of the plastic material between the rods and the exterior
surface of the plastic, i.e. such involves a matter of design
choice. Thus, the method of the present invention provides for
positively creating a tight contact between metal and plastic after
the molding together thereof rather than simply attempting to rely
on the plastic and metal initially forming a tight bond there
between solely as a result of the molding process itself. It has
been found that such post molding linear translation bonding
process between metal and plastic is extremely effective in
creating contact there between that is highly liquid and gas proof.
In the example of sensor 10, water and carbon dioxide gas are
prevented from flowing along the surfaces of rods 14 and 16 between
those surfaces and body 12, even where the interior of carbonator
tank 33 is pressurized. Thus, such water and gas can not find their
way to rod ends 14b and 16b and ultimately out of tank 33. It can
also be understood that the plurality of surfaces 70 along the
length of each rod 14 and 16 provide for a multiplicity of solid
areas of contact around the circumference of each rod, thereby
providing a redundancy in such contact should any one annular are
of contact fail.
Because water will not find its way to ends 14b and 16b the
possibility of that water resulting in an electrical shorting
contact there between, the problems associated therewith of
inaccurate or faulty readings will be greatly reduced or
eliminated. Such shorting contact can also arise from condensation
on ends 14b and 16b. Such condensation occurs because carbonator 10
is generally cooled well below ambient temperatures and thereby
cools sensor 10. Also sensor 10 will generally be positioned in an
area of relatively high humidity. Thus, it can be seen that flanges
40, 42 and 44 are positioned and structured to interrupt the
formation of a continuous liquid contact between rod ends 14b and
16b.
An alternate embodiment of a rod as used in the present invention
can be seen in FIG. 9. As seen therein, a rod 82 includes a
plurality of barbs 84, and corresponding narrowed waist areas 85.
Each barb 84 has an annular conical surface 84a, and a shoulder
surface 86 having outer perimeter edges 87 and an inner perimeter
edge 88. The primary difference being that rod 82 is manufactured
by roll forming thereof. Thus, pressure is applied at each waist
area 88 displacing material that forms barbs 84. Embodiment 82
works in the same manner as that disclosed in rods 14 and 16
whereby translation of rod 82 in the direction of Arrow B in FIG. 9
provides for the surfaces 84a wedging against the plastic material
formed there around.
A further rod embodiment is seen in FIG. 10 and referred to by the
numeral 100. Rod 100 is also roll formed wherein the upset material
forms a plurality of barbs 102 directly adjacent each other at one
end of rod 100. In one embodiment of the present invention
utilizing rod embodiment 100, the probe body plastic material is
formed around rod 100 and barbs 102, after which rod 100 is then
translated after cooling in the direction of arrow C. In a further
embodiment, not shown, the plastic material is not formed around
barbs 102, and after cooling of the plastic material, barbs 102 are
all pulled therein.
It can be understood by those of skill that the essence of the
present invention is to have an elongate piece of metal, such as a
rod, that is to be sealed in a liquid and gas tight manner within a
plastic body. This is accomplished with a plurality of annular
intrusions or protrusions forming annular plastic displacing means
around the circumference thereof that provide for a sealing contact
between the sealing means and the surrounding plastic material that
forms the housing. The sealing results from a post-cooling linear
translation of the elongate rod with respect to the surrounding
plastic material whereby the displacing means is forced into and
moves the plastic material adjacent thereto resulting in a gas and
liquid tights seal between the displacing means and the plastic
material. Therefore, water or gas under pressure can not flow along
the rod between it and the plastic material. The inclined plane
portion of the rods serves to mechanically assist in the displacing
of the plastic material in a manner that is conducive to forming a
complete seal around the entire circumference of each annular
displacing means. Those of skill will understand that the number of
such displacing means within a housing will be a matter of design
choice. And those of skill will also recognize that a wide variety
of shapes of annular protrusions and/or intrusions along an
elongate metal object can provide for such sealing whereby the
intrusion or protrusion will cause movement of the plastic material
and sealing there between as the result of relative motion between
the two.. It can be further appreciated by those of skill that a
wide variety of sizes and dimensions of the elongate metal objects
such as rods 14,16 and 82 can be had. In a carbonator level sensing
embodiment of the present invention, such rods can have a nominal
diameter of 0.0935 inch where the difference between that diameter
and the height or depth of an annular protrusion or intrusion
respectively is on the order of 0.0085-0.0065 inch. In the
application of a sensor such as sensor 10, rods 14 and 16 are
inserted within body 12 approximately 3/16 inch after cooling of
the plastic material. A wide variety of plastic materials are known
and useful in various applications where molding around a metal
object and sealing there between is required and would be
applicable to the method and structure of the present invention. In
the case of a liquid level sensor used in a carbonator of a
beverage dispensing device, plastics such as polycarbonate,
polyester or polyethylene are used.
* * * * *